SWIFT HEAVY-ION MODIFICATION OF POLYMERS

We have studied the effects of dense electronic excitations on vinyl l inear polymers, by performing swift heavy ion, SHI, irradiations. We u sed different ion beams, from C to Pb, provided by the GANIL accelerat or at energies of a few MeV/u. We mainly studied the physico-chemical modifications induced in polyethylene (PE), but the role of chemical s ubstitutions has also been investigated by studying the swift heavy io n induced damage in polyvinylidene fluoride (PVDF) and polystyrene (PS ). The irradiated samples were analysed ex-situ by means of Fourier tr ansform infrared spectroscopy in the transmission mode. Any contact wi th air was avoided: oxidation does not occur. Swift heavy ion irradiat ions are characterised by a significant increase of the yield of chain scission associated with unsaturated end groups. Moreover, we have ev idences for specific modifications, i.e. modifications which are never observed when using low ionising particles as electrons or gamma-rays ; namely the creation of alkyne and allene end groups. These specific modifications are little sensitive to chemical substitutions. For inst ance, alkyne formation is observed in PE, PVDF and PS. A simultaneous ionisation of the different atoms of a constituting monomer is likely needed for triggering the formation of the specific swift heavy ion in duced modifications. On the other hand, if we pay attention to the phy sico-chemical modifications which are easily induced by low ionising p articles, it is observed that increasing the electronic stopping power does not significantly modify the creation yield of, for instance in PE, trans-vinylene or trans-trans diene groups.